The most common and widely used high speed mail inserters are of the "Phillipsburg-type", having initially been introduced in the late 1920's. U.S. Pat. No. 2,325,455 discloses such a mail insertion device. In normal operation of these inserters, a suction cup rotates into engagement with a lowermost sheet, in a stack of film or paper. The cup then rotates away from the stack, drawing with it a single, segregated sheet. A reciprocating picker arm, provided with a pivotally mounted gripper jaw on its lower end, rotates into a first position, adjacent an edge of the segregated sheet. The gripper jaw then rotates into a closed position, seizing the single sheet of film. With the film in its grasp, the picker arm next rotates into a second position, where the jaw rotates open and the sheet is deposited upon a conveyor. The picking cycle is repeated, successively delivering individual sheets in a continuous fashion.
A typical mail inserter will have a plurality of such picker arm stations, arranged in a row overlying the conveyor. Each picker arm, and the associated sheet segregating components, is dedicated to a particular stack of sheets or film inserts. The conveyor is successively indexed beneath each picker arm, for collating the proper number and types of sheets. After the sheets are properly assembled, they are inserted into envelopes for mailing.
Two persistent and recurrent fault conditions occur in everyday use of this prior art, "Phillipsburg-type" machine. In the mail inserter industry, these fault conditions are respectively termed "doubles" and "misses". For example, if the suction cup concurrently draws two or more sheets away from the same stack, a "double" will occur unless this fault condition is detected and corrected. Likewise, if the suction cup fails to pull down a sheet from the stack during a picking cycle, a "miss" will occur, unless detected and corrected.
To detect these fault conditions, the prior art device includes a dual contact switch on the picker arm. A movable arm of the switch is attached to the same drive shaft which pivots the gripper jaw open and closed. Accordingly, with the jaw closed, the position of the switch arm is determined by the thickness of the sheet, if any, holding the jaw partially open. In this manner, a "double" deflects the switch arm into one extreme position against one contact, and a "miss" deflects the switch arm into an opposite extreme position against the other contact. Manually actuated adjustment screws are provided for both switch contacts, so that each will make contact with the arm at predetermined positions corresponding to a fault condition.
In the event of either fault condition arising, a signal is sent to a main control relay, immediately and completely shutting down the entire machine, until the condition is corrected.
Over a period of time, the pivot shaft for the gripping jaw and their associated bearings become worn. This wear causes the prior art system to read faults conditions erratically, and makes the switch contacts difficult to set properly. The switch contact points also become oxidized and highly resistive, making electrical contact erratically or not at all. Machine operators often forget to readjust the "double" detect switch contact when sheets or inserts of different thicknesses are loaded into the machine. This maladjustment, for example, allows a "double" of thinner inserts mistakenly to be detected as acceptable in thickness. All of these problems lead to unnecessary stops and undermine the production efficiency of the inserter.
Over the years, some efforts have been made to modernize these intensely mechanical mail insertion devices, which have numerous cams, chains, gears, drive shafts, bearings, and electro-mechanical switches. For example, in U.S. Pat. No. 4,634,107, a gripper jaw including an electrical solenoid for actuating the movable jaw member, is disclosed. The '107 Patent also shows a pair of magnets mounted to the movable jaw member and a Hall Effect sensor on the picker arm. The sensor produces a signal proportional to jaw displacement. However, since the bearings supporting the movable jaw and the magnets are subject to wear over a period of time, this arrangement may also lead to unreliable and inefficient operation.
By eliminating and redesigning many of the mechanical and the electro-mechanical components of the prior art devices, the invention described herein enjoys improved reliability in operation and higher "throughput" in pieces handled. The invention includes an improved sensor system for the gripper jaw which is highly accurate and not susceptible to wear-induced inaccuracies or unreliability. Certain cams, shafts, and gears of the prior art machine are replaced with pneumatic drivers, controlled by a computer and programmable software. The present invention also provides new operational features in mail inserter machines, with its computer gathering, storing and processing current information about the operating parameters of each gripper jaw assembly. The computer software disclosed herein further makes logic decisions and issues control signals, which, for example, outsort envelopes containing defective insert packages.